In general it is well known to provide spade drills in which a blade is clamped in a holder. Examples of this are shown, for example, in U.S. Pat. No. 3,076,357 and British Pat. No. 1,270,068. The blades that are used in this type of holder are generally provided with lateral edges that are cylindrically ground to provide a guide surface which engages the side of the hole being drilled and to prevent entire engagement these edges are sometimes relieved a certain amount as shown in U.S. Pat. No. 3,076,357. This, however, does not take care of all of the camming and heeling actions.